1. Field of the Invention
The present invention relates to an apparatus of controlling to rotate a step motor for driving to rotate a step motor and detecting presence or absence of rotation of the step motor.
2. Description of the Prior Art
Conventionally, there has bee used a step motor as a motor for driving to rotate a time hand or the like in an electronic timepiece.
FIG. 2 is a constitution view of a step motor conventionally used in an electronic timepiece. In FIG. 2, a step motor is provided with a stator 401, a coil 307 wound around the stator 401 and a rotor 402 of two poles arranged at inside of the stator 401. The stator 401 is formed with saturable portions 403 and 404.
When a drive pulse of a rectangular wave is supplied to the coil 307 and current i is made to flow in an arrow mark direction of FIG. 2, magnetic flux is generated in an arrow mark direction in the stator 401. Thereby, the saturable portions 403 and 404 are firstly saturated, thereafter, by interactive operation of a magnetic pole produced at the stator 401 and a magnetic pole of the rotor 402, the rotor 402 is rotated by 180 degrees in the counterclockwise direction. Thereafter, by making current having different polarities flow alternately to the coil 307, the above-described similar operation is carried out and the rotor 402 is rotated in the counterclockwise direction by 180 degrees respectively.
FIG. 3 and FIG. 4 are circuit diagrams showing an apparatus of controlling to rotate a step motor conventionally used in an electronic timepiece, constituting a circuit integrally constituted with a rotation drive circuit and a rotation detection circuit. FIG. 3 is an explanatory view of operation when the step motor is controlled to rotate by the rotation drive circuit and FIG. 4 is an explanatory view when rotation of the step motor is detected by the rotation detection circuit. Further, FIG. 5A shows a drive pulse used in driving to rotate the step motor and FIG. 5B shows a control pulse for detecting rotation used in detecting rotation of the step motor.
In FIG. 3 and FIG. 4, P-channel MOS transistors 301 and 302 and N-channel MOS transistors 303 and 304 are constituent elements of a motor drive circuit and a coil 307 of a step motor is connected between a point of connecting sources of the transistor 301 and the transistor 303 and a point of connecting sources of the transistor 302 and the transistor 304.
Meanwhile, N-channel MOS transistors 303 through 306, a resistor 308 for detection connected in series with the transistor 305 and a resistor 309 for detection connected in series with the transistor 306 and a comparator 310 are constituent elements of the rotation detection circuit.
Gates of the respective transistors 301 through 306 are connected in a control circuit 312.
A point OUT2 for connecting the resistor 308 for detection and the coil 307 and a point OUT1 for connecting the resistor 309 for detection and the coil 307 are connected to an input portion of the comparator 310. Further, the input portion of the comparator 310 is inputted with threshold voltage Vss.
In the above-described constitution, when a drive pulse P1 of FIG. 5A is supplied to an input portion Vi of a control circuit 312, by control of the control circuit 312, as shown by FIG. 3, the transistors 302 and 303 are brought into an ON state. Thereby, current is made to flow to the coil 307 in an arrow mark direction and as shown by FIG. 2, the rotor 402 is rotated in the counterclockwise direction.
Meanwhile, there is provided a rotation detection period for detecting whether the step motor is rotated, immediately after a motor drive period.
During the rotation detection period, the input portion Vi of the control circuit 312 is supplied with rotation detection control pulse SP1 of FIG. 5B. In response to the rotation detection control pulse SP1, as shown by FIG. 4, the control circuit 312 controls to make the transistor 304 to ON/OFF in a state of making the transistors 303 and 306 ON.
At this occasion, detection voltage is outputted from the connection point OUT1 of the resistor 309 for rotation detection and the coil 307. As the detection voltage, there is provided a signal having a waveform as shown by FIG. 7(a). In FIG. 7(a), there is generated detection voltage on a lower side of VDD when the rotor 42 is oscillated in the counterclockwise direction and there is generated detection voltage on an upper side of VDD when the rotor 42 is oscillated in the clockwise direction.
When the rotor 402 is rotated, there is provided detection voltage equal to or lower than predetermined threshold voltage (Vss according to the conventional example) and a rotation detection signal Vs at a high level is outputted from the comparator 310. When the rotor 402 is not rotated, the detection voltage is not equal to or lower than the threshold voltage and therefore, the rotation detection signal Vs at a low level is outputted from the comparator 310. Whether the step motor is rotated, can be detected from the rotation detection signal Vs. After detection of rotation has been finished, the transistors 303 and 304 are maintained in an ON state to thereby brake the step motor.
At a successive motor drive period, the following normal drive pulse P1 is supplied to the input portion Vi of the control circuit 312. The control circuit 312 controls the transistors 301 and 304 to an ON state and drive current in a direction reverse to that of the drive current (direction reverse to the arrow mark of FIG. 3) is made to flow at the coil 307 and the rotor 402 is rotated in the counterclockwise direction.
During the rotation detection period at this occasion, when the rotation detection control pulse SP1 is supplied to the input portion Vi of the control circuit 312, the transistors 304 and 305 are controlled to ON and the transistor 303 is controlled to ON/OFF. At this occasion, detection voltage is outputted from the connection point OUT2 of the resistor 308 and the coil 307 and a level thereof is determined by the comparator 310. Similar to the above-described,when the rotor 402 is rotated, the rotation detection signal Vs at the high level is outputted from the comparator 310 and when the rotor 402 is not rotated, the rotation detection signal Vs at the low level is outputted from the comparator 310. Whether the motor is rotated, can be detected from the rotation detection signal Vs. When detection of rotation has been finished, the transistors 303 and 304 are brought into an ON state to thereby brake the step motor.
According to the step motor having the above-described constitution, after the rotor 402 is driven by the drive pulse P1, the rotor 402 is freely oscillated centering on a position at which the rotor 402 is to be stopped. Immediately after finishing the drive pulse P1, free oscillation of the rotor 402 is considerable, further, by inertia, the rotor 402 is oscillated in a direction the same as a regular rotational direction (counterclockwise direction in the above-described conventional example). When the rotor 402 is oscillated in the counterclockwise direction, in FIG. 4, current is made to flow in the arrow mark direction.
Meanwhile, as shown by FIG. 6, an equivalent circuit of the respective transistors 303 through 306 is constituted by a series circuit of a switch 501 and a resistor 502 and a diode 503 and a capacitor 504 respectively connected in parallel with the series circuit and the respective transistors 303 through 306 are equivalently regarded as an element having a diode in one direction.
Therefore, even when the step motor is not rotated, within a predetermined period IT immediately after finishing the drive pulse P1, oscillation of the rotor 42 in the counter direction is considerable and therefore, as shown by FIG. 7(a), there is a case in which detection voltage equal to or lower than the threshold voltage Vss is provided. Thereafter, when the rotor 42 is oscillated in the clockwise direction, current is made to flow in the direction reverse to the arrow mark of FIG. 4 and owing to influence of the diode component, there is provided detection voltage restricted to a constant level on a side opposed to the threshold voltage Vss centering on VDD. Thereafter, the above-described operation is repeated.
That is, according to the detection voltage provided in the predetermined period IT immediately after finishing the drive pulse P1, regardless of whether the motor is rotated, detection voltage having a large peak value is produced at the resistor 309 for detection by large free oscillation of the rotor 402 and there poses a problem that it is erroneously detected that the step motor is rotating.
Conventionally, in order to resolve the problem, the rotation is not detected during the predetermined period IT immediately after finishing the drive pulse P1 and the rotation detection operation is carried out after elapse of the period IT. Although it can be prevented to erroneously detect nonrotation as rotation thereby, the period IT differs by the characteristic of the step motor and therefore, the period IT needs to be set for the respective motor and there poses a problem that selection of a material, arrangement or the like of a part becomes extremely complicated.
It is a problem of the invention to prevent erroneous detection when a step motor is not rotated by a simple constitution.
According to the invention, there is provided an apparatus of controlling to rotate a step motor characterized in that in an apparatus of controlling to rotate a step motor comprising a first and a second switch element connected in series, a third and a fourth switch element connected in series, a coil of the step motor connected between a point of connecting the first and the second switch elements and a point of connecting the third and the fourth switch elements, a first series circuit comprising a fifth switch element and a first element for detection connected in parallel with the first switch element, a second series circuit comprising a sixth switch element and a second element for detection connected in parallel with the third switch element, controlling means for driving to rotate the step motor by making a current flow to the coil by controlling the first through the fourth switches in response to a drive pulse and controlling the first, the third, the fifth and the sixth switch elements in response to a control pulse for detecting rotation supplied immediately after finishing the drive pulse, and determining means for determining presence or absence of rotation of the step motor based on a result of comparing a voltage produced between the first and the second elements for detection and the coil and a threshold voltage wherein the controlling means makes ON the fifth or the sixth switch element on a side of producing a detection voltage in a direction reverse to a direction of the threshold voltage with a predetermined voltage as a reference between the first and the second elements for detection and the coil immediately after finishing the drive pulse, controls to make ON/OFF the first switch element after bringing the third switch element to an ON state when the fifth switch element is brought into the ON state and controls to make ON/OFF the third switch element after bringing the first switch element to the ON state when the sixth switch element is brought into the ON state, and the determining means determines presence or absence of the rotation of the step motor based on the result of comparing the voltage produced between the first element for detection and the coil and the threshold voltage when the fifth switch element is brought into the ON state and determines presence or absence of the rotation of the step motor based on the result of comparing the voltage produced between the second element for detection and the coil and the threshold voltage when the sixth switch element is brought into the ON state.
The controlling means makes ON the fifth or the sixth element for detection on the side of producing the detection voltage in the direction reverse to the direction of the threshold voltage between the first and the second elements for detection and the coil immediately after finishing the drive pulse, controls to make ON/OFF the first switch element after bringing the third switch element to the ON state when the fifth switch element is brought into the ON state and controls to make ON/OFF the third switch element after bringing the first switch element to the ON state when the sixth switch element is brought into the ON state. The determining means determines presence or absence of rotation of the step motor based on the result of comparing the voltage produced between the first element for detection and the coil when the fifth switch element is brought into the ON state and determines presence or absence of the rotation of the step motor based on the result of comparing the voltage produced between the second element for detection and the coil and the threshold voltage when the sixth switch element is brought into ON state.
Further, there may be constructed a constitution in which the first, the third, the fifth and the sixth switch elements are constituted by N-channel MOS transistors and the second and the fourth switch elements are constituted by P-channel MOS transistors.
Further, the first and the second elements for detection may be constituted by resistors.